3S Basin Flows

The 3S basin Flow model simulates flows in the Se San, Sre Pok, and Sre Kong rivers by simulating basin hydrology, hydropower operations, and routing of water. This model was developed using HEC-ResSim and SWAT (Piman et al., 2012) for the following scenarios:

Baseline scenario (BL): reference river flow scenario resembling natural conditions. No hydropower projects are included in this scenario.

Definite future scenario (DF): includes existing and ongoing hydropower construction projects that are expected to occur in the near term (next 5 years). This scenario includes 19 projects (8 existing and 11 projects under construction).

Development on main tributaries scenario (DMT): future hydropower development on the main 3S Rivers (Mekong tributaries) that countries have considered for study or development. This scenario comprises the developments in the DF plus the proposed developments on the main 3S Rivers, totalling 28 projects (8 existing, 11 under construction and 9 proposed projects).

Development on main and sub tributaries scenario (DMST): all current and proposed hydropower development on the main 3S Rivers and sub tributaries. This scenario comprises the developments in the DMT plus the proposed developments on the sub tributaries, totalling 41 projects (8 existing, 11 under construction, 9 proposed projects on the main 3S Rivers and 13 proposed projects on the sub tributaries).

In addition to the level of dam development, three operation rules which define target water levels for each reservoir were modelled to compare resulting changes in power plant releases and downstream flows:

Seasonal variation rule: consists of setting seasonal water release targets from the reservoir. The rule fluctuates the reservoir in order to maximize seasonal energy production, avoid running the reservoir dry before the end of the dry season, and minimize the risk of excess spillage due to the reservoir being full before the end of the wet season. The water release decision of this operation is dependent on the reservoir target level and the physical plant release capacities related to the reservoir levels. If the water levels in the reservoir are lower than target levels, the dam operator will stop flows through the turbines to raise water levels in the reservoir.

full level rule: consists of trying to keep the reservoir at full levels (ecological flows)

low level rule: consists of trying to keep the reservoir at low levels (mitigation of flooding)

All these are also simulated under three climatic conditions:

Historical climate 1986 - 2006

Climate change scenario A2

Climate change scenario B2

These scenarios aim to show the possible range of dam operations and their effect on electricity production, power plant releases and flow patterns.